j. luyten, k. sniegowski, k. van eyck, d. maertens, s ... 1...chloride (mg/l) 750 650 1500 aox (µg...
TRANSCRIPT
AOX removal from industrial wastewaters using Advanced
Oxidation Processes: assessment of a combined chemical-
biological oxidationbiological oxidation
J. Luyten, K. Sniegowski, K. Van Eyck, D. Maertens, S.
Timmermans, Sven Liers and L. Braeken
Introduction and problem description
AOX = Adsorbable Halogenated Organic Compounds (Group parameter)
= Hazardous / toxic organic pollutants
= Source: mostly industrial production
→ Decreasing discharge limits (EU water framework directive 2000/60/EC)
AOX + AOP (O3, H2O2/UV, O3/UV Fe(II)/H2O2)→ Degradation products(Parilti et al., Perez et al.,Kusic et al.)
AOPs increase the biodegradability of waste water streams(Van Aken et al., Ballesteros et al., Guo et al.)
Presence of halogenated ions ( Cl-, Br-,…) jeopardises the use of AOPs(Baycan et al., Sniegowski et al.)
1
2
AOX+oxidant degradation products
COD+oxidant degradation products
k
k
→
→
Industrial waste water: halogenated compounds (AOX) ↔ matrix compounds (COD)
Introduction and problem description
→ Selective AOX degradation is requested
→ Reaction order might change during experiments (especially with O3)
→ Oxidant dose is a key parameter for removal efficiency
Potential of a combined chemical and biological oxidation for removal of
AOX in industrial waste waters?
Sensitivity of AOX removal on operational parameters?
Methods and materials
100% Ozone : 16 g O3/h
100% UV: 2000 W
100% H2O2: 2 mg H2O2 / mg COD
Pilot scale plant : Volume 50 L
Medium pressure Hg lamp, Philips
[Fe2+]/[H2O2] ratio of 1/100 ww
Sample 1 Sample 2 Sample 3
Chloride (mg/l) 750 650 1500
AOX (µg Cl/l)
(discharge limit)
1500 (400) 5000 (400) 10000 (1000)
pH 7,8 7,9 8
Methods and materials
• Biological oxidation (4h): Respirometry experiments using 500 ml waste water
and 300 ml communal WWTP activated sludge (300 ml), periodically aerated.
• AOX measurements according WAC/IV/B/011 protocol, ThermoFischer
Scientific 3000 systems TN/TS/TX (SphiNCX)
• Nanocolor® COD reactor and Nanocolor® 500 D colorimeter from Machery Nagel
Different halogenated compounds,
Batch production
Specific compound
Results waste water I
60,00%
70,00%
80,00%
90,00%
100,00%
AO
X/A
OX
0 %
AOX removal after different AOPs
O3/UV pH9
O3/UV pH7
O3/UV50 pH7
0,00%
10,00%
20,00%
30,00%
40,00%
50,00%
60,00%
0 20 40 60
AO
X/A
OX
Reaction time (min)
O3/UV50 pH7
O350/UV pH7
UV/H2O2 42% belucht pH7
UV/H2O2 31% belucht pH9
UV/H2O2 25% onbelucht pH7
Fotofenton 25%
Fotofenton 56%
UV
Results waste water I
60,00%
70,00%
80,00%
90,00%
100,00%
AO
X/A
OX
0 %
AOX after respiration (4h) at different AOP reaction time
O3/UV pH9
O3/UV pH7
O3/UV50 pH7
0,00%
10,00%
20,00%
30,00%
40,00%
50,00%
0 20 40 60
AO
X/A
OX
AOP reaction time (min)
O3/UV50 pH7
O350/UV pH7
UV/H2O2 belucht pH7
UV/H2O2 belucht pH9
UV/H2O2 onbelucht pH7
Fotofenton 25%
Fotofenton 56%
UV
Results: waste water I
30,00%
40,00%
50,00%
60,00%
70,00%
80,00%
90,00%
100,00%
AO
X/A
OX
0(%
)
Discharge
limit
• Biological oxidation of the original wastewater : ± 20%.
• Ozone based techniques: 50 % removal after 60 minutes, more biodegradable than
H2O2 based techniques
• UV alone: 50% AOX, slightly biodegradable
0,00%
10,00%
20,00%
Chemical
Biological
Final AOX
limit
Results: Selectivity coefficient
Technique AOX0 AOXf COD0 CODf Overall selectivity
S(AOX/COD)
O3/UV pH 9 1647 804 206 184 4.9
O /UV pH 7 1700 894 184 102 1.1
For H2O2-based experiments no selectivity parameter is reported
Varying H2O2 results in similar AOX and COD removal efficiencies.
• Ozone based AOP can selectively degrade AOX towards COD
• Selectivity: O3(50%)/UV > O3/UV > O3/UV(50%)
→ lower ozone concentration with respect to UV intensity is recommended
• Increasing the pH to 9 enhances the selectivity for AOX removal
O3/UV pH 7 1700 894 184 102 1.1
O3/UV(50%), pH 7 1517 847 177 94 0.9
O3 (50%)/UV, pH 7 1660 631 170 93 1.4
Results: Effect of UV intensity and H2O2 dose
UV intensity
(kW)
Oxidant + dose
(g/h)
AOX0 (µg
Cl/l)
AOX (µg Cl/l)
after AOP (60
min)
AOX (µg Cl/l) after
biological
oxidation (4 h)
0.25 H2O2 /6.79 4130 4401 3382
0.5 H2O2 /6.79 4110 3835 2835
0.5 H2O2 /3.4 4908 4106 3388
2.0 H2O2 /6.79 5493 4572 3358
• O3/UV at pH 7 leads to an increase in (biodegradable) AOX
• H2O2-based techniques: high UV intensity and intermediate H2O2 dosage is requested.
• Variable effluent concentrations demand strict monitoring as the discharge limit is not
reached within 60 minutes reaction time (+ biodegradation) due to high initial AOX level
2.0 H2O2 /6.79 5493 4572 3358
2.0 H2O2 /4.53 4640 1707 1658
2.0 H2O2 /2.5 5355 2506 1880
1.0 H2O2 /6.79 5283 3357 2358
2.0 O3/ 16 4438 4748 2205
Results: Sensitivity of operational parameters
AOX removal by UV/H2O2 at pH 7
• Reaction time and H2O2 dose should be balanced in order to avoid AOX formation.
• Optimal: H2O2 dosage of 3-4.5 g corresponding with a reaction time of 50-60 min.
Results: Sensitivity of operational parameters
AOX removal by UV/H2O2 at pH 7
• Best results: UV power between 1 - 2 kW
• Optimal combination of reaction time and UV intensity is crucial!
Conclusions
• AOX can be significantly reduced in industrial wastewater by a combined
chemical-biological treatment. Monitoring is crucial with variable effluent
composition.
• Oxidant concentration is a key parameter for selective degradation of AOX
towards COD
• For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better • For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better
selectivity for AOX.
• O3-based AOPs remove less AOX than H2O2-based AOPs but increases the
biological degradable fraction more.
• Reaction time, H2O2 dose and UV intensity needs to balanced for optimal AOX
removal.